Process of preparing metal sheets for annealing



Patented ay 3, 1932 rs S it LOUIS C. DREFAHL, 01F LAKEWOOD, OHIO, ASSIGNOR TO THE GRASSELLI CHEMICAL COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF DELAW PROCESS OF PREPARING METAL SHEETS FOR ANNEAJL-aba No Drawing.

In the production of sheets of ferrous metals the following is the usual procedure: Sheet bars are heated to a designated temperature in a heating furnace and subsequently rolled in the usual manner, the sheets being passed through rolls successively, either individually or in packs to reduce the sheets to the desired gaugeQ The sheets are then sheared to the desired size and pickled'for the removal of mill scale. In order to fit the sheet metal for subsequent operations and to take out stresses due to rolling and also for the removal of possibly occluded gases, the pickled sheets are given a heat treatment ordinarily called annealing. The pickled sheets are, while still wet, stacked up sheet to sheet, without spacers, and put in the usual type of annealing box provided for this purpose. This annealing box is then transferred into a furnace where such box and contents are heated to the desired degree for a designated period of time. Temperatures customarily used are 1280 to 1300 F., and complete cycle of annealing is about 24 hours. It is the experience that when the annealing has been practiced in this manner, the superimposed sheets stick to one another, making vit diflicult and sometimes even impossible to tear the sheets asunder, often resulting in damage to the sheets and often making it necessary to waste a considerable portion of the same.

I have found that such sticking of the sheets can be prevented or greatly minimized if the sheets, before annealing, have on their surface a very small deposit of a water soluble substance which does not substantially undergo any chemical reaction under annealing conditions, and my invention is directed to a process of'preparing metal sheets for annealing, in which the sheets to be annealed are treated with a water soluble substance which does not substantially undergo any chemical change under annealing. v

The substances which substantially do not react under annealing conditions are mostly neutral, mineral salts, such as sodium sulfate, sodium chloride, sodium carbonate, sodium phosphate, sodium borate, as well as other Application filed March 17, 1930. Serial No. 436,643.

similar compounds. They are all easily soluble in water.

The most convenient manner of forming a deposit of such non-reactive substances on the sheets is to pass the sheets through an aqueous solution of the substance or to spray the sheets with such a solution and pack the sheets wet, annealing them in the customary manner. It is, of course, also possible to dry out the solution on the sheets before annealing. When the sheets so treated are taken out of the annealing furnace it will be found that they separate very easily and not at all in the manner whichv is common with the sheets obtained in ordinary, prior practice. There is substantially no pitting or attack noticeable on the sheets when using substances of the type mentioned above.

I found, for instance, that when wetting pickled and Washed sheet metal of the ferrous type with an aqueous 4% sodium sulfate solution the sheets came out of the annealing furnace perfectly, without any sticking together or damage to the sheets. Solutions of lower concentrations will have a similar elfect and, of course, solutions of higher concentration will produce the same result, and it would appear that within a reasonable range the concentration of the solution is immaterial. 1 Similar concentrations of the other substances can be used, and again the same results are obtained. The sheets after a first annealing are sometimes submitted to further operations, such as cold rolling, then also submitted to a gentle pickling known as white pickle, and lightly reannealed'preparatory to other operations, among which may be tinning.

In depositing a substance of the type speci- 'fied above on the sheet metal before the first an insoluble residue on such sheet; such insoluble residue would probably work into the sheet metal and not be removed by the subse uent white pickle.

%Vhile the second annealing, after white pickle, is at considerably lower temperature than the first annealing, it might, in many instances, be desirable to again deposit such a non-reactive substance on the sheets to pre- 16 Vent sticking. Whatever residue might be left on the sheets would hardly be noticeable and would not interfere with the subse-. quent tinning or galvanization and be removed at that time.

I claim:

1. In a process of manufacturing sheets of ferrous metals which comprises operations of rolling, pickling and annealing, the step of coating the pickled sheets with a dilute 20 solution of sodium sulfate, and annealing said coated sheets.

2. In a process of manufacturing sheets of ferrous metals which comprises operations of rolling, pickling and annealing, the step of coating the pickled sheets with a dilute solution of sodium compound selected from the group of sodium salts consisting of sodium sulfate, sodium chloride, sodium carbonate, sodium phosphate and sodium borate, and annealing said coated sheets.

In testimony whereof, I aflix my signature. LOUIS C. DREFAHL. 

